1. Field of the Invention
The present invention relates to a flat panel display device and a fabrication method thereof and, more particularly, to a flat panel display device comprising an electrostatic discharge protection unit capable of discharging static electricity generated in the flat panel display device without damaging a thin film transistor (TFT), and a method of fabricating the flat panel display device.
2. Description of Related Art
A cathode-ray tube (CRT) is a commonly used display device, which is mainly used in monitors, televisions, measuring instruments, information terminals, etc. However, a CRT is not capable of actively coping with requirements for leaner and lighter electronic products due to its weight and size.
A flat panel display device having the merits of a small size and light weight has attracted attention for replacing the CRT. Types of flat panel display devices include liquid crystal displays (LCD), organic light-emitting displays (OLED), etc.
A flat panel display device includes a substrate on which a thin film transistor (TFT) is formed, and red, green, and blue light-emitting diodes.
The foregoing flat panel display device is formed mainly through a TFT array process of forming a TFT for applying signals to pixel units, a process of forming red, green and blue light-emitting diodes for materialization of colors, and a process of cutting the TFT substrate into cells of unit flat panel display devices.
The process of cutting the TFT substrate into cells of the unit flat panel display devices includes a process of scribing cutting lines on the TFT substrate after forming the light-emitting diodes thereon, and a process of cutting the TFT substrate along the cutting lines by applying force to the cutting lines.
The flat panel display device is typically fabricated on an insulation substrate such as a glass substrate, and the insulation substrate is very weak to static electricity since it is a nonconductor. The insulation substrate is a nonconductor in order to prevent an electric charge from generating instantaneously and discharging to the lower side of the substrate. Therefore, an insulation film, TFT or light-emitting diodes formed on the insulation substrate can be damaged by static electricity.
In this case, the substrate may become partially degraded since static electricity has characteristics of very high voltage and very low electric charge amount. Furthermore, static electricity is generated mainly in a cell cutting process of cutting the substrate. Most of the static electricity flows in through a pad part of gate lines and data lines, and degrades the channels of the TFT.
Typically, a shorting bar is installed at a region surrounding a pixel region to prevent static electricity from degrading the TFT after static electricity flows in from the outside as described in the above.
Low temperature polycrystalline silicon having a superior crystalline structure is commonly used as a semiconductor layer of a TFT. However, the low temperature polycrystalline silicon has a characteristic in which morphology is deteriorated on grain boundaries. FIG. 1 is a photograph showing a portion A of a gate electrode of a TFT where low temperature polycrystalline silicon 10 is partially projected. As shown, the gate insulation film 20 is damaged because its thickness at the projected portion is thin, and static electricity is discharged from this thin portion when static electricity is generated.
FIG. 2 is a photograph showing a TFT damaged by static electricity. A portion B is defective where wires largely overlap due to generation of static electricity. In addition to this portion, a plurality of defects due to static electricity are generated on other portions on which an electric field is concentrated due to bent wirings.
FIG. 3A is a schematic plan view illustrating a conventional organic electroluminescence display device. FIG. 3B is another schematic plan view illustrating a part of an ordinary organic electroluminescence display device. FIG. 3C is a photograph showing a floating scan line installed from the left side to the right side. Scan signals going through scan lines shown in FIGS. 3A-3C are applied to the left side and completed at the right side, and parts C of the scan lines where the scan signals end are floating.
FIG. 4 is a drawing illustrating a defect map of an organic electroluminescence display device according to prior art and showing that defects due to static electricity are mainly generated on the right sides of the scan lines where scan signals of FIG. 3A end. Static electricity is discharged to the floating end parts C of the scan lines to which an electric field is concentrated or to a weak part of the device. This static electricity results in defects of the device. The static electricity is generated at a starting point of the scan lines and is transmitted to the opposite side of the starting point inside the organic electroluminescence display device.
The foregoing flat panel display device according to the prior art has problems of lower reliability and lower yield of the device, including damage of TFT caused by static electricity, since a protection unit for handling electrostatic discharge is not applied to the inside of a pixel region of a small flat panel display device. This is because a static electricity circuit occupies a large area although a shorting bar is formed on a region surrounding the pixel region to prevent the device from being damaged by static electricity flowing in from the outside.